1. Field of the Invention
The present invention is concerned with the improvements in room temperature control apparatus in a heater wherein heated air is fed in forced convection in a room by an air blower.
2. Discussion of Background
The room temperature control in such type heater is generally carried out by use of one temperature detector which is arranged in the heater casing. The temperature control will be explained in reference to FIG. 9. FIG. 9 is an electrical circuit diagram of the room temperature control unit in a conventional heater. In FIG. 9, reference numeral 1 designates the heater, and reference numeral 2 designates a main switch. Reference numeral 3 designates the combustion chamber in the heater 1 where e.g. kerosene is burnt as fuel. Reference numeral 4 designates an air blower which is mounted on the rear side of the heater 1 to circulate in the room the heated air produced by the combustion in the combustion chamber 3. Reference numeral 5 designates a temperature detection element which is constituted by a thermistor or the like to detect a temperature in the room. Reference numeral 7 designates an A/D (analog/digital) converter which converts the present resistance value of the temperature detection element 5 in a digital value. Reference numeral 9 designates an operation switch which is used for a user to input his or her sensation to the temperature in the room at the present time. The operation switch is constituted by a "cold" button 19 switch which is depressed when the user feels cold, a "comfortable" button 20 switch which is depressed when the user feels comfortable, and a "hot" button 21 switch which is depressed when the user feels hot, as shown in FIG. 12. Reference numeral 10 designates a microcomputer which includes a set room temperature determining means and an air volume determining means. The microcomputer also includes an input circuit 11, a CPU 12, a memory 13 and an output circuit 14. The input circuit 11 receives the output from the operation switch 9 and a signal indicative of a room temperture through the A/D converter 7. The output circuit 14 transmits a signal to a heating capability control device 15 to control the combustion output of the combustion chamber 3 in the heater 1 (hereinafter, referred to as heating capability). The output circuit 14 also transmits a signal to an air blower control device 16 to control the air volume (revolution) of the air blower 4 of the heater 1.
Now, the operation of the heater will be explained in reference to FIG. 10. FIG. 10 is a flow chart including a program which is stored in the memory 13 of the microcomputer 10 and determines the set temperature, the heating capability and the air volume.
First, when the main switch 2 is turned on, the flow of FIG. 10 starts. When the user uses the heater 1 for the first time after having bought it, the heating operation starts targetting the set temperature which has been prestored in the memory 13 before shipment. After the user has used the heater once, the temperature which was detected by the temperature detection element 5 when the "comfortable" button 20 has been actuated at the time of the previous heating operation is stored in the memory 13 as a set temperature. At a Step S101, the room temperature Tr detected by the temperature detection element 5 is input. At a Step S102, it is checked whether the sensation input by the operation switch 9 is made or not. If affirmative, the process proceeds to a step S103. The Step S103 through a Step S106 are a flow as the set room temperature determining means. When the Step S102 finds that the user has not input his or her sensation, the flow of the Step S103-S106 is skipped, and the process proceeds to a flow of a Step S107 and the subsequent steps as the heating capability determining means and the air volume determining means. When the Step S103 judges that the sensation input selected by the user is "cold", the set room temperauture is reset to a value which is obtained by adding a.degree. C. (e.g. 2.degree. C.) to the present room temperature Tr to determine a new set room temperature Tc at the Step S104. When the Step S103 judges that the sensation input selected by the user is "hot" , the set room temperature is reset to a value obtained by substracting a.degree. C. from the detected room temperature Tr to determine a new set room temperature Tc at the Step S106. When the Step S103 judges that the sensation input is "comfortable", the Step S105 makes the set room temperature equal to the detected room temperature Tr to determine a new set room temperature Tc. At a Step S107, the temperature difference .DELTA.T between the new set room temperature Tc and the detected room temperature Tr is calculated. The heating output needed is determined at a Step S108, and the air volume is determined at a Step S109, thereby to carry out the heating operation. The heating capability is determined so that it is proportional to the temperature difference between the new set room temperature and the detected room temperature. For example, when the detected room temperature is higher than the set room temperature, the heater 1 is controlled to be turned off so as to make the room temperature equal to the set room temperature. The air volume is determined so that it is proportional to the heating capability as shown in FIG. 11. For example, the heater is controlled so that as the room temperature approaches the set room temperature, the air volume decreases. This is because uncomfortable air flow in the room is minimized, and because the outlet air temperature is kept constant. In this way, the temperature condition in the room is controlled so that the room temperature is made equal to the set room temperature while the heating capability and the air volume are changing.
The conventional heater carries out the room temperature control while it is resetting the set room temperature, and changes the heating output and the air volume according to the sensation input selected by the user as explained. The purpose of heaters is to allow a person in the room to feel comfortable. The sensation of a person in the room is mainly influenced by the temperature at his or her feet and the temperature at his or her head. The temperature distribution in the vertical direction in the room with a heater in it is formed so that the temperature at an upper portion of the room is higher and the temperature at a lower portion and on the floor of the room is lower depending on the specific gravity difference of air. The temperature distribution in the vertical direction is determined depending on agitation power caused by the air feed of the heater. That is to say, when the air volume is great, the variation in the temperature distribution is lower, whereas when the air volume is small, the variation in the temperature distribution is larger. In addition, the temperature distribution is also influenced by the temperature outside the room. That is to say, when the temperature outside increases, the variation in the temperature distribution is smaller, whereas when the temperature outside decreases, the variation in the temperature distribution is larger.
The air volume of the conventional heater is dependent on the heating capability, i.e. is determined to be dependent on the temperature difference between a detected room temperature and a set room temperature. This means that the air volume is controlled irrespectively of the difference between the temperatures at an upper level and at a lower level in the room which has the greatest influence to sensation of a person in the room. As a result, when the temperature outside the room has changed, or when the air volume has changed at the time of having input sensation or because of the change in the room temperature, a person in the room feels uncomfortable due to the changed temperature conditions around him or her.